h bridge design, technical question about transistors

[weeb0]

h bridge transistors

Hello,

I'm about to build an H bridge for a buzzer.

I find the following circuit very interesting, but I will not use the opto-coupler.

I was wondering why the pnp transistor were at the top ? I build one from myself and I putted the pnp at the bottom of the circuit...

Do somebody can explain me if there is any advantage for each placement of the pnp / npn transistor ?

thank you a lot!
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[Tammam17]

h bridge design

Hello,

I'm about to build an H bridge for a buzzer.

I find the following circuit very interesting, but I will not use the opto-coupler.

I was wondering why the pnp transistor were at the top ? I build one from myself and I putted the pnp at the bottom of the circuit...

Do somebody can explain me if there is any advantage for each placement of the pnp / npn transistor ?

thank you a lot!
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hey.

I dont what your question is exactly .. but i know from experience that placing those transistors the wrong way you will easily cook the circuilt ... why are you building a H-brigde from descrete components anyways ... i would suggest you get the LM293D H Bridge IC. it is the exact same thing as the circuit you show exept it is capable of controlling two motors.

 

[amriths04]

transistor h bridge

If you put pnp at bottom and npn at top (and appropriately swap there biasing through opto-couplers),

1) Just think what would be the voltages at the motor terminals during operation.
2) Think what would happen to your switch resistances. (Do they act like a switch and would they be able to operately easily in the required regions).

Hope that helps.

 

[Kral]

h bridge with npn pnp transistor

weeb0,
PNP transistors are used in the "top" of a bridge, so that they can be driven without the use of a separate power supply for the drive. If NPNs were used on top, then they would have to be used in the emitter follower configuration which necessitates a supply voltage more positive thatn the bridge power. Also, you would always have a Vbe drop inherent in the emitter follower configuration.
Regards,
Kral